1. Field of the Invention
The present invention relates to negative dobbies of the type incorporating swinging levers, intended for controlling the heddle frames on weaving machines.
2. Description of the Related Art
It is known that, in dobbies of the type referred to above each heddle frame is actuated against the action of springs or other elastic means which tend to return the frame to one of the two ends of its reciprocating vertical stroke. As illustrated schematically in FIG. 1 of the accompanying drawings, which figure is a schematic transverse section of a conventional dobby, each heddle frame C is coupled to a cable and/or a drawing arm 1 to a suspension lever 2 articulated at 3 on the frame 4 of the dobby. A connecting rod 5 joins each lever 2 to a lever assembly 6 supporting a lever element, the lever assembly 6 being pivotally supported on a common pivot pin 7; each lever assembly lever 6 is equipped at its free end with a lever element 8 provided at its ends with articulated hooks 9.
In order to swing each lever element 8 about its pivot pin 10 carried by the corresponding lever 6, there is provided an actuating mechanism comprising two crosspieces 11 which are carried by two lateral rocking elements 12 so as to bear against the bead of the hooks 9. Any actuating mechanism, formed for example by arms 13 coupled to the rocking elements 12 and fitted in eccentric manner on a transverse shaft 14, imparts to the rocking elements a continuous rocking movement about their fixed pivot 15.
In conventional constructions, each of the two articulated hooks 9 carried by each level element 8 is sectioned so as to cooperate with a corresponding retaining member 16 in the form of a hook, which pivots about a common pivot pin 17 under the effect of a reading device 18 of the type incorporating pegs or punched paper, which device contains the weaving program for making the fabric desired.
From the practical standpoint, this embodiment presents appreciable drawbacks.
It will firstly be observed that, due to the respective positioning of pieces 9 and 16 of each pair, combined with the orientation of the fastening faces of such pieces, these latter work in bending, with the result that, in order to avoid any bending having regard to the considerable efforts to which said pieces are subjected in operation, large sections must be provided which obviously increase the masses that the reading device 18 must maneuver. Consequently, the springs associated with the hooks 16 (referenced 16a in FIG. 1), or incorporated in the device 18 must be more powerful; at the same time, the selection time (i.e. the operational rhythm of the reading device) must be extended, which reduces the speed of the dobby.
Moreover, and as illustrated more precisely in FIG. 2 of the accompanying drawings, which figure shows on a large scale the the lower hook of one of the lever elements 8 of a conventional dobby, the unfavourable path of the pieces 9 and 16 makes it necessary to provide greater strokes for ungripping or disengaging the members which slow down the operational speed of the dobby. Effectively, concerning the horizontal displacement of each hook 9, ungripping, i.e. the distance that said hook must cover beyond the hooked position in order to allow its disengagement from the corresponding hook 16, is equal, not to the value d1 corresponding solely to the operational clearance, but to value d2 due to the obliqueness necessarily given to the bearing faces of the hooks.
Such increase in the ungripping or disengages stroke must be taken into account both at the level of the actuating mechanism 13-14 associated with the crosspiece-supporting rocking elements 12 and at the level of the reading device 18, with the result that it has a detrimental influence on the operational speed of the dobby.